Vibration reduction in mechanical systems is important for a number of reasons including safety and energy efficiency of the systems. Particularly, vibration in various transportation systems is directly related to ride quality and safety of passengers, and, thus, should be minimized. For example, vertical vibration in vehicles can be controlled by active or passive vibration reduction systems, which are generally referred as suspension systems. Similarly, the vibration induced during an operation of an elevator system can be minimized.
The elevator system typically includes a car, a frame, a roller guide assembly, and guide rails. The roller guides act as a suspension system to minimize the vibration of the elevator car. The car and roller guides are mounted on the frame. The car and frame move along the guide rail as constrained by the guide rollers. There are two principal disturbances which contribute to the levels of vibration in the car: (1) rail-induced forces which are transferred to the car through the rail guides due to rail irregularities, and (2) direct-car forces, such as produced by wind buffeting the building, passenger load, distribution or motion.
Some methods, e.g., methods described in U.S. Pat. Nos. 5,289,902, 5,712,783, 7,909,141,8,011,478, compensate for irregularity of the guide rail in the elevator system to improve the comfort of the ride. However, those methods do not consider uncertainties in the elevator components, for instance the parameters of a damping device changes over time due to aging, temperature, and thus reduce the effectiveness of the vibration reduction suspension system.
For example, U.S. Pat. No. 5,289,902 discloses a method to control actuators damping the vibration of the elevator car by comparing the frequency of a vibration signal to a pre-determined frequency. The pre-determined frequency is calibrated based on fixed values of parameters of the elevator and actuators.
Because parameters of the elevator and actuators may vary over time, new values of parameters may correspond to a different pre-determined value to maintain a desirable performance on vibration reduction. A controller that fails to acquire the variations of parameters deteriorates the performance of the method.